This invention relates generally to cooling structure for battery cells within a battery pack, and more particularly to coupling a battery cell to a cooling frame with integral attachment features to simultaneously promote adequate clearance between the cell and frame during high volume battery pack assembly and sealing of a fluid introduced into a space defined between the cell and the cooling frame once the battery pack has been assembled.
Lithium-ion and related batteries, collectively known as a rechargeable energy storage system (RESS), are being used in automotive and related transportation applications as a way to supplement, in the case of hybrid electric vehicles (HEVs), or supplant, in the case of purely electric vehicles (EVs), conventional internal combustion engines (ICEs). The ability to passively store energy from stationary and portable sources, as well as from recaptured kinetic energy provided by the vehicle and its components, makes such batteries ideal to serve as part of a propulsion system for cars, trucks, buses, motorcycles and related vehicular platforms. In one form suitable for automotive applications, individual battery cells (i.e., a single electrochemical unit) are shaped as generally thin rectangular members. The flow of electric current to and from the cells is such that when several such cells are combined into larger assemblies, the current or voltage can be increased to generate the desired power output. In the present context, larger module and pack assemblies are made up of one or more cells joined in series, parallel or both, and may include additional structure to ensure proper installation and operation of these calls. Although the term “battery pack” is used herein to discuss a substantially complete battery assembly for use in propulsive power applications, it will be understood by those skilled in the art that related terms—such as “battery unit” or the like—may also be used to describe such an assembly, and that either term may be used interchangeably without a loss in such understanding.
Temperature is one of the most significant factors impacting both the performance and life of a battery, especially those used in propulsive power for vehicular applications and related high power-demand configurations. Exogenously, environmental conditions (such as those encountered during protracted periods of inactivity in cold or hot environments) are significant factors, while endogenously, the large amounts of electrical energy and concomitant heat generation produced by battery packs, as well as abuse conditions (such as the rapid charge/discharge, or internal/external shorts caused by the physical deformation, penetration, or manufacturing defects of the cells), can negatively impact the ability of the battery to operate correctly. In extreme forms of either case, such temperatures can destroy the battery entirely. With particular regard to prolonged exposure high temperatures, side effects may include premature aging and accelerated power and energy fade, both of which are additionally undesirable.
In one form, the individual cells that make up a battery pack are configured as rectangular (i.e., prismatic) cans that define a rigid outer housing known as a cell case. As with their similarly-shaped prismatic pouch cell counterparts, prismatic can-style cells can be placed in a facing arrangement (much like a deck of cards) along a stacking axis formed by the aligned parallel plate-like surfaces. Positive and negative terminals situated on one edge on the cell case exterior are laterally-spaced from one another relative to the stacking axis and act as electrical contacts for connection (via busbar, for example) to an outside load or circuit. Within the cell case, numerous individual alternating positive and negative electrodes are spaced apart from one another along the stacking direction and kept electrically isolated by non-conductive separators. Leads from each of the negative electrodes are gathered together inside the cell case to feed the negative terminal, while leads from each of the positive electrodes are likewise gathered together to feed the positive terminal.
To help avoid the buildup of excessive heat, cooling systems may be integrated into the battery pack. In the configurations described above—where the battery cells are stacked or arranged in a generally repeating manner—such cooling systems may include means for introducing a cooling medium between individual battery cells. The operation of such cooling systems may be hampered by the expansion and related compressive action of the battery cells in response to temperature increases, as cooling channels that may be present during lower pack temperature tend to reduce in size (or be cut off altogether) in response to individual cell expansion. To prevent the temperature-related problems, frame-like members for holding, mounting or otherwise securing adjacently-stacked battery cells may be used to maintain the channels or related volumetric space formed between them. As such, these frames are often critical to maintaining the dimensional consistency and related sealing integrity between adjacent cells as a way to prevent the inadvertent release of the cooling medium being introduced into the channels or related interstitial volumes. Despite this, the attachment and sealing associated with coupling the frames to the cells requires complicated manufacturing processes. With prismatic can cell configurations in particular, the placement of a cooling frame adjacent a battery cell can have mutually-exclusive interests. For example, trying to ensure a suitably high level of sealing integrity through tight dimensional tolerances hampers high-speed assembly operations, whereas high assembly throughput leaves larger manufacturing tolerances that in turn lead to gaps between the cell and frame that are responsible for most of the coolant losses within the pack.